The sleep switch that builds muscle, burns fat, and boosts brainpower

As every bodybuilder knows, a deep, restful sleep boosts levels of growth hormone to build strong muscle and bone and burn fat. And as every teenager should know, they won’t reach their full height potential without adequate growth hormone from a full night’s sleep.

But why lack of sleep — in particular the early, deep phase called non-REM sleep — lowers levels of growth hormone has been a mystery.

In a study published in the current issue of the journal Cell, researchers from University of California, Berkeley, dissect the brain circuits that control growth hormone release during sleep and report a novel feedback mechanism in the brain that keeps growth hormone levels finely balanced.

The findings provide a map for understanding how sleep and hormone regulation interact. The new feedback mechanism could open avenues for treating people with sleep disorders tied to metabolic conditions like diabetes, as well as degenerative diseases like Parkinson’s and Alzheimer’s.

“People know that growth hormone release is tightly related to sleep, but only through drawing blood and checking growth hormone levels during sleep,” said study first author Xinlu Ding, a postdoctoral fellow in UC Berkeley’s Department of Neuroscience and the Helen Wills Neuroscience Institute. “We’re actually directly recording neural activity in mice to see what’s going on. We are providing a basic circuit to work on in the future to develop different treatments.”

Because growth hormone regulates glucose and fat metabolism, insufficient sleep can also worsen risks for obesity, diabetes and cardiovascular disease.

The neurons that orchestrate growth hormone release during the sleep-wake cycle — growth hormone releasing hormone (GHRH) neurons and two types of somatostatin neurons — are buried deep in the hypothalamus, an ancient brain hub conserved in all mammals. Once released, growth hormone increases the activity of neurons in the locus coeruleus, an area in the brainstem involved in arousal, attention, cognition and novelty seeking. Dysregulation of locus coeruleus neurons is implicated in numerous psychiatric and neurological disorders.